Bieber, 18, posted pictures on his public Instagram account of Pacquiao, 34, flat on his stomach after being knocked down by Marquez.

In one photograph, a photoshopped image of the Disney character Simba was seen leaning over Pacquiao, with the caption, "Dad wake up".

In another mock image, late singer Michael Jackson is pictured in his famous leaning pose from the Smooth Criminal video, mirroring the stance of Pacquiao just before he hit the floor of the boxing ring.

Indignation over Bieber's insult reached the Philippines Congress, with seven law-makers filing a resolution demanding an apology from the singer for the "distasteful comments … lest he be declared persona non grata".

"Mr. Bieber should have known that the Hon. Pacquiao has reached his stature as such as a result of sheer hard work, determination and firm belief in God, and despite such stature best exemplifies humility and grace even in defeat," the congressmen said.

They added that it was not only Pacquiao who Bieber insulted, but also the entire population.

Pacquiao released a statement saying he would pray for Bieber.

Bieber - who is known for pop hits such as Boyfriend, and whose fans are referred to as "Beliebers" - addressed the issue on his social media account: "If they were Beliebers I know they wouldn't leave my side over [a] boxing opinion I have."